Stabilized inertial navigation apparatus, such as that employed for self contained, high precision airborne applications, typically include a platform whereon a number of gyroscopes and accelerometers are mounted and three or more gimbals are required for stabilizing the platform. For a pure inertial or free inertial navigator the dominant source of navigation error is the gyro drift or platform reference drift error. Since the platform provides an inertial reference, this drift can be substantially eliminated by tracking stellar objects. Consequently, for astro-inertial operation, additional apparatus may include a telescope and an imager, such as a vidicon tube, for imaging and tracking stellar objects such as stars. Also, two or more gimbals, typically azimuth and elevation, are required to point the telescope. During astro-inertial navigation, the dominant sources of navigation error are horizontal accelerometer errors and gravity anomalies. Gravity modeling, for high precision astro-inertial navigation, has reduced these errors to be consistent with high precision accelerometer performance.
Several problems associated with conventional high accuracy, free inertial navigators include: a) excessive size and cost due to the three or gimbals required to stabilize the instrument cluster and, b) a relatively large position error growth which is typically greater than 0.2 nautical mile per hour.
Several problems associated with conventional high accuracy astro-inertial navigators include: a) excessive size and cost due to the number of gimbals required to stabilize the instrument cluster and to point the telescope and b) the cost of the ultra-high precision (arc second) -resolvers, and their associated calibration requirements, which are required to transform the star line, or telescope line-of-sight, measurements to the inertially stabilized instrument cluster.
Additionally, airborne stabilized platforms require the use of gimbal slip rings which increase system cost and complexity and reduce system reliability.